Heat exchanger for wall furnace

ABSTRACT

A counterflow, forced air, gas-fired, vented wall furnace includes a combustion chamber having a gas burner at its lower end and a wall defining a vertically extending duct for the flow of hot flue gases. The vertically extending duct feeds the hot flue gases through a pair of holes into a draft hood chamber, the holes being positioned between a relief opening for drawing fresh air into the flow of hot flue gases and a secondary heat exchanger which receives hot flue gases from the draft hood chamber. A baffle shielding wall extends from the relief opening partially over the holes to deflect the flow of hot flue gases toward the secondary heat exchanger. A vertically disposed baffle wall extends between the top wall of the draft hood chamber downwardly between the draft hood chamber and the secondary heat exchanger. The lower edge of this wall defines an opening to the secondary heat exchanger, the vertical baffle wall serving to deflect the flow of hot flue gases downwardly into the secondary heat exchanger to a point well below the relief opening. From this point, the hot flue gases flow upwardly to a furnace vent pipe. The furnace also includes an air flow system including a blower for forcing air in a direction counter to the direction of the flow of the hot flue gases over the combustion chamber, the draft hood chamber, and the secondary heat exchanger to extract heat from the hot flue gases for warming the air to be warmed. A heat responsive switch is responsive to the temperature of the air to be warmed and energizes the blower when the temperature reaches a predetermined level.

United States Patent 11 1 1111 3,841,301

Chamberlain Oct. 15, 1974 HEAT EXCHANGER FOR WALL FURNACE nace includes a combustion chamber having a gas burner at its lower end and a wall defining a vertically [751' Inventorfigfimgh gz Stone extending duct for the flow of hot flue gases. The vertically extending duct feeds the hot flue gases through Asslgneei The Atlanta Stove Works, a pair of holes into a draft hood chamber, the holes a being positioned between a relief opening for drawing fresh air into the flow of hot flue gases and a secon- [22] Flled' 1973 dary heat exchanger which receives hot flue gases PP 336,201 from the draft hood chamber. A baffle shielding wall extends from the relief opening partially over the holes to deflect the flow of hot flue gases toward the 126/110 secondary heat exchanger. A vertically d1sposed baffle [58] Fie'ld B H6 wall extends between the top wall of the draft hood ll 10 chamber downwardly between the draft hood chamber and the secondary heat exchanger. The lower edge [56] References Cited of this wall defines an opening to the secondary heat exchanger, the vertical baffle wall serving to deflect UNITED STATES PATENTS the flow of hot flue gases downwardly into the secon- R dary heat exchanger to a point well below the relief S opening. From this point, the hot flue gases flow up- 2808047 10/1957 J l 126]]16 R wardly to a furnace vent p1pe. The furnace also 1n- 2884048 4/1959 ig i 26/110 R cludes an air flow system including a blower for forc- 219231287 2/1960 Murphy....... 126 110 R ing a direction Counter to the direction of 31255604 6/1966 Bedell et al. 126/110 R flow 0f the hot flue gases Over the Combustion Chum- Primary Examiner--Carroll B. Dority, Jr. Assistant Examiner-W. E. Tapolcai, Jr.

- Attorney, Agent, or Firm-Newton, Hopkins &

Ormsby [57] ABSTRACT A counterflow, forced air, gas-fired, vented wall furber, the draft hood chamber, and the secondary heat exchanger to extract heat from the hot flue gases for warming the air to be warmed. A heat responsive switch is responsive to the temperature of the air to be warmed and energizes the blower when the temperature reaches a predetermined level.

5 Claims, 3 Drawing Figures min m am 1 51m MATC/l L/A/E 70 1 76. 2/1

FIG 2A FIG 2B A G I HEAT EXCHANGER FOR WALL FURNACE BACKGROUND OF THE INVENTION This invention relates to heat exchangers and, more particularly, to heat exchangers for gas fired, counterflow, wall furnaces.

It is frequently not possible or convenient to locate a furnace in a separate room or basement. For this reason, wall furnaces, which are mounted directly on the wall of a room to be heated, have become popular.

Typically, furnaces of this character are of the counterflow, forced air, gas fired, vented type in which a combustion chamber provides an inner duct for the upward flow of hot flue gases. Such furnaces are provided with a relief opening for drawing fresh air into the flowing hot fuel gases to promote upward flow thereof into a secondary heat exchanger system. A duct system for the air to be warmed is provided, and a blower forces the air to be warmed in a direction opposite to the flow of the gases in contact with the walls of the combustion chamber duct and secondary heat exchanger to extract heat therefrom.

The longer the hot gases are held in the combustion chamber-secondary heat exchanger system and the greater contact they have with all of the walls of the system, the greater will be the heat transfer to the air to be warmed and the greater will be the efficiency of the system. However, burned gases can be held in the combustion chamber a limited amount of time and must be discharged and replaced by other gases from the continuing combustion process on the burners. If the burned gases are held too long in the combustion chamber or if their flow is too slow, the burner flame will tend to smother and incomplete combustion with resulting poisonous gases will occur.

Although this problem can be solved by providing a combustion chamber-secondary heat exchanger system of greater vertical height, it is also desirable to hole the height of the wall furnace to a minimum so that it will have maximum flexibility in fitting the walls of rooms with low ceilings. While the vertical height of the furnace can be reduced by reversing the path of flow to the secondary heat exchanger, this introduces the danger that flue gases will spill out of the relief opening. Such draft hood spillage is not normal and is to be avoided.

SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide an improved heat exchanger system for a wall furnace.

More specifically, it is an object of the invention to provide a counterflow, forced air, gas fired, vented wall furnace having maximum efficiency and minimum height. A related object is the provision of a system of this character which avoids spillover of flue gases through the relief opening of the draft hood.

To this end, the invention contemplates the provision of baffle means in association with the draft hood assembly which will divert the flow of hot fuel gases rearwardly from the relief opening and downwardly into a secondary heat exchanger to a point well below the bottom of the relief opening, the baffle means being so designed that it prevents spillover of flue gases from the relief opening.

Briefly, a wall furnace according to the invention, comprises a combustion chamber including a wall defining a vertically extending duct for the upward flow of hot flue gases from burners positioned at the bottom of the combustion chamber. A draft hood assembly includes a relief opening for drawing fresh air into the flowing flue gases and provides a draft hood chamber between the relief opening and a secondary heat exchanger which conducts the flue gases to an outlet vent pipe. The flue gases from the combustion chamber are received into the draft hood chamber through openings in the bottom wall of the draft hood chamber located between the relief opening and the secondary heat exchanger. Baffle means are provided for deflecting the flowing hot flue gases rearwardly to the secondary heat exchanger and downwardly into the secondary heat exchanger to a point well below the bottom of the relief opening, the baffle means serving to prevent spillover of flue gases from the relief opening. More specifically, the bafile means includes a horizontal baffle plate extending rearwardly from the relief opening partially over the holes from the combustion chamber and a vertical baffle plate extending downwardly from the upper wall of the draft hood chamber between the draft hood chamber and the secondary heat exchanger to provide an opening between the lower edge of the vertical baffle plate and the bottom wall of the draft hood chamber. The furnace additionally includes a duct system for the flow of the air to be warmed about the combustion chamber, the draft hood assembly, and the secondary heat exchanger. The flow of the air is forced in a direction counter to the direction of the flow of the flue gases by a blower which is energized by a heat responsive switch positioned in the duct system for the air to be warmed.

These and other features, objects, and advantages of the invention will become more readily apparent upon consideration of the following detailed description of a preferred embodiment of the invention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a wall furnace of the invention;

FIG. 2A is a partial, enlarged section view taken along the lines 2 2 of FIG. I; and

FIG. 2B is a partial, enlarged section view taken along the lines 2 2 of FIG. 1, FIGS. 2A and 28 being joined at the indicated match line.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a wall furnace 10 embodying the invention is shown. The furnace is enclosed within a housing 12 which is adapted to be mounted on a wall of a room to be heated. As will be presently explained, the vertical height of the housing is maintained at a minimum without sacrificing efficiency so that the unit may be employed in rooms having a relatively low ceilmg.

The front wall of housing 12 is, near its upper end, provided with a louvered opening 14 which serves as an inlet for the air to be warmed. After the air to be warmed is heated in the furnace, it is discharged from an outlet opening 16, also covered by a louvered grill. Air to supplant combustion is drawn to the burners of the furnace through a louvered opening 18. A louvered opening is provided to draw air to the relief opening of a draft hood assembly for feeding fresh air to flue gases from a combustion chamber of the furnace. At the top of the furnace an outlet opening 22 is provided for connection to a furnace vent pipe (not shown). I

Turning to FIGS. 2A and 2B, which together represent a cross-section along lines 2 2 of FIG. 1, it will be noted that a pair of gas burners 24 are provided at the lower end of housing 12. A fuel gas is fed to burner 24 through a gas pipe 26 and mixes with primary air inside burners 24. The gas is ignited by a pilot burner (not shown) and burns to form a gas flame 28. During the combustion process, additional air 30 is drawn through opening 18 and supplied to flame 28 as secondary air. Hot flue gases 32 will then flow upwardly from flame 28, being confined within a combustion chamber 34. Combustion chamber 34, which serves as a vertical duct for the upward flow of hot flue gases 32, is enclosed within a rectangular wall 36 formed of a metal having high thermal conductivity and includes a lower, relatively wide section 38 and a tapered section 40 serving as a transition to a relatively narrow section 42. Combustion chamber 34 serves as a primary heat exchanger and, thus, is provided with means for enhancing heat transfer through wall 36. This means includes the provision of ribs 44 in wall 36 in the lower section 38 and dimples 46 indented in wall 36 in the upper section 42 which increase the surface area through which heat is transferred. Although dimples 46, as shown in FIGS. 2A and 2B, are shown as meeting midway across section 42 of combustion chamber 34, it will be understood that dimples 46 do not block the flow of hot flue gases and that vertical passageways are provided adjacent the dimples.

Wall 36 of combustion chamber 34 is supported at its lower end by a rib 48 serving as a shoulder resting upon a transverse wall 49 surrounding an opening provided through wall 49 which receives the lower end of wall 36. The upper end of combustion chamber 34 is provided with an enlarged end section 50 having a vertical side wall 51 connected to section 42 by means of a horizontal shoulder 52. On one side, side wall 51 is bolted to a flange 54 provided at the upper end of an inclined wall 56 serving as the bottom wall of a relief opening 70 of a draft hood assembly 68 to be described more fully hereinafter. On the other side of section 50, side wall 51 is bolted to a flange 58 extending upwardly from a shoulder 59 provided at the top of a wall 60 forming one side of a lower portion 102 of a secondary heat exchanger 96 to be described more fully hereinafter. In order to restrict the flow of hot flue gases from section 42 of combustion chamber 34 so that the hot flue gases are retained for a longer period of time within combustion chamber 34, a plate 61, which is narrower than the opening 62 from section 42, is supported on shoulder 52 and is bridged across opening 62, partially obstructing the opening, and leaving a pair of openings 64 for the flow of hot flue gases on either side thereof. Plate 61 is provided with an upstanding flange 63 by means of which it is bolted to the inner surface of side wall 51 opposite to its connection toflange 58. Thus, a pair of openings, or holes, are provided for the flow of the hot flue gases from section 42 of combustion chamber 34 to a draft hood chamber 66.

Draft hood chamber 66 is included within a draft hood assembly 68 and extends between relief opening 70 provided behind louvered grill 20 and secondary heat exchanger 96. Relief opening 70 is defined by a duct section including lower wall 56, an inclined upper wall 72, and side walls (not shown). Lower wall 56 includes a lower flange 76 which is bolted to a housing frame member 78.

Draft hood assembly 68 includes a shielding baffle duct 80 which is formed by an upper wall 82 which is supported between flanges 84 and 86 depending from a horizontal structural wall section 88 extending across the housing. Shielding baffle duct 80 also includes a lower wall 90 which is mounted on the other side of flange 54 and extends partially over openings 64 to deflect hot flue gases entering chamber 66 from combustion chamber 34 through holes 64 rearwardly towards the secondary heat exchanger. Duct section 80 also includes a pair of side walls, one of which 92 is shown.

Draft hood chamber 66 extends between relief opening 70 and a vertical baffle wall 94 which extends downwardly from the top of chamber 66- between chamber 66 and secondary heat exchanger 96. It will be noted, therefore, that openings 64 are positioned between relief opening 70 and secondary heat exchanger 96 and may be considered as extending through a lower wall of chamber 66. The lower edge 98 of baffle wall 94 defines an opening 100 between it and shoulder 59 forming the rear edge of the lower wall of chamber 66. Opening 100 serves as an entrance port to secondary heat exchanger 96, and specifically to a lower portion 102 thereof. This lower portion 102 extends downwardly to a point 104 well below the lower edge of relief opening 70. Secondary heat exchanger 96 also includes a vertical duct 106 which extends upwardly from lower portion 102 to outlet opening 22. As described above, outlet opening 22 is connected to a furnace vent pipe (not shown).

The air to be warmed is provided with a separate duct system 110 which is formed in the space surrounding combustion chamber 34, draft hood assembly 68, and secondary heat exchanger 96. A heat responsive switch 112 is mounted on a bracket 114 supported on housing frame member 78 within duct 110. After ignition of the gas flame within combustion chamber 34, heat is transferred through wall 36 to duct space 1 l0 heating switch 112 until it closes at a predetermined temperature to energize air blower 1 16 which is mounted at the top of housing 12 adjacent inlet opening 14. Air 118 is then drawn through the louvered opening 14 and blown under pressure from blower 116 at 120 through air duct system 1 10. It will be understood that the air to be warmed will wipe the outer surfaces of secondary heat exchanger 96, draft hood assembly 68, and combustion chamber wall 36 to extract heat therefrom. The warmed air 122 is then blown out through louvered opening 16 and returned to the room to be heated.

The operation of the furnace will be readily understood. Gas enters bumers 24 through pipe 26 and is ignited by a pilot burner to form flame 28. During the combustion process, additional air 30 is supplied to the flame as secondary air and hot flue gases 32 flow upwardly through combustion chamber 34 within the duct created by chamber wall 36. Heat is transferred through wall 36 to the air in air duct 110, the transfer of heat being enhanced by the greater surface of ribs 44 and dimples 46. When enough heat is built up around combustion chamber 34 within duct 110, switch 112 closes to energize blower 116; and room air 118' is drawn into the blower and forced downwardly over the hot combustion chamber 34 and secondary heat exchanger 96 thereby picking up heat from these hot chambers. The warmed air is then discharged as heated air through opening 16.

Hot flue gases 32 are discharged from combustion chamber 34 through openings 64 into draft hood chamber 66 where they are diluted by being mixed with room air 130 drawn through louvered opening and relief opening 70. Although the hot flue gases are somewhat cooled by this mixing they are still substantially hot as they enter secondary heat exchanger 96 through opening 100. The lower wall 90 of baffle shielding duct 80 serves to deflect the hot flue gases entering chamber 66 through openings 64 rearwardly toward secondary heat exchanger 96. in addition, vertical baffle wall 94 serves to deflet the hot flue gases 32 downwardly through opening 100 into the lower portion 102 of secondary heat exchanger 96. After reaching a point well below draft hood relief opening 70, the hot flue gases then flow upwardly through the upper portion 106 of secondary heat exchanger 96 and through outlet opening 22. The provision of shielding baffle duct 80, and particularly the position of lower wall 90 thereof, serve to prevent spilling of hot flue gases out of relief opening 70 into the room. The deflection of the flow of the hot flue gases downwardly to lower point 104 of secondary heat exchanger 96 extends the time the hot flue gases are maintained within the heat exchanger system, thereby increasing the efficiency of the heat exchanger. Since the hot gases are circulated lower than the relief opening of the draft hood assembly after they pass the draft hood assembly, they are held in the system the maximum possible time. This arrangement provides maximum efficiency for a minimum overall height of the furnace.

While a preferred embodiment of the invention has been shown and described, it will be readily apparent to those skilled in the art that changes can be made without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims.

The invention claimed is:

1. A heat exchanger for a warm air furnace comprismg:

a combustion chamber including a wall defining a vertically extending duct for the flow of hot flue gases;

a draft hood assembly for receiving hot flue gases from said combustion chamber, said draft hood assembly including a relief opening for drawing fresh air into said flow of hot flue gases and baffle means for deflecting said flow of hot flue gases and fresh air downwardly into a secondary heat exchanger to a point lower than said relief opening, said secondary heat exchanger extending upwardly from said point to provide a path for the flow of said flue gases to a flue vent opening, said draft hood assembly including a draft hood chamber positioned between said relief opening and said secondary heat exchanger, said draft hood assembly including a substantially horizontal bottom wall extending rearwardly from the lowest margin of said relief opening into partial overlapping relation only with respect to the upper end of said flue gas duct of the combustion chamber and terminating in a rear edge, said draft hood assembly also including a top wall extending rearwardly beyond said rear edge of said bottom wall, and said baffle means comprising a baffle plate extending downwardly from said top wall of the draft hood assembly and terminating in a lower edge disposed rearwardly of and above said rear edge of the bottom wall to define an opening between said rear edge and said lower edge leading downwardly into said secondary heat exchanger, said bottom wall and said baffle plate cooperating to prevent spilling of hot flue gases back through said relief opening; and

means for conveying air to be warmed in contact with the outside of said wall defining said vertically extending duct, the outside surface of said draft hood assembly, and the outside surface of said secondary heat exchanger, whereby heat from said hot flue gases will be transferred to said air to be warmed as it passes over said combustion chamber, draft hood assembly, and secondary heat exchanger.

2. A heat exchanger according to claim 1 wherein said means for conveying said air to be warmed comprises a blower.

3. A heat exchanger according to claim 2, further comprising heat responsive switch means for energizing said blower when the temperature of said air to be warmed reaches a predetermined level.

4. A heat exchanger according to claim 1 wherein said air to be heated flows in a direction opposite to the direction of flow of said flue gases.

5. A heat exchanger according to claim 1, further comprising combustion means at the lower end of said combustion chamber creating a flame burning a fuel gas to create said hot flue gases. 

1. A heat exchanger for a warm air furnace comprising: a combustion chamber including a wall defining a vertically extending duct for the flow of hot flue gases; a draft hood assembly for receiving hot flue gases from said combustion chamber, said draft hood assembly including a relief opening for drawing fresh air into said flow of hot flue gases and baffle means for deflecting said flow of hot flue gases and fresh air downwardly into a secondary heat exchanger to a point lower than said relief opening, said secondary heat exchanger extending upwardly from said point to provide a path for the flow of said flue gases to a flue vent opening, said draft hood assembly including a draft hood chamber positioned between said relief opening and said secondary heat exchanger, said draft hood assembly including a substantially horizontal bottom wall extending rearwardly from the lowest margin of said relief opening into partial overlapping relation only with respect to the upper end of said flue gas duct of the combustion chamber and terminating in a rear edge, said draft hood assembly also including a top wall extending rearwardly beyond said rear edge of said bottom wall, and said baffle means comprising a baffle plate extending downwardly from said top wall of the draft hood assembly and terminating in a lower edge disposed rearwardly of and above said rear edge of the bottom wall to define an opening between said rear edge and said lower edge leading downwardly into said secondary heat exchanger, said bottom wall and said baffle plate cooperating to prevent spilling of hot flue gases back through said relief opening; and means for conveying air to be warmed in contact with the outside of said wall defining said vertically extending duct, the outside surface of said draft hood assembly, and the outside surface of said secondary heat exchanger, whereby heat from said hot flue gases will be transferred to said air to be warmed as it passes over said combustion chamber, draft hood assembly, and secondary heat exchanger.
 2. A heat exchanger according to claim 1 wherein said means for conveying said air to be warmed comprises a blower.
 3. A heat Exchanger according to claim 2, further comprising heat responsive switch means for energizing said blower when the temperature of said air to be warmed reaches a predetermined level.
 4. A heat exchanger according to claim 1 wherein said air to be heated flows in a direction opposite to the direction of flow of said flue gases.
 5. A heat exchanger according to claim 1, further comprising combustion means at the lower end of said combustion chamber creating a flame burning a fuel gas to create said hot flue gases. 